The present invention relates to a method and a device for transferring data between storage units, and more particularly to a method and device which may suitably apply to data transfer between a disk cache memory and a disk drive in a disk subsystem having a cache memory.
For the conventional disk subsystem, a disk cache memory has been proposed in JP-A-55-154650 for copying a part of the data stored in a disk drive to a semi-conductor memory and improving the access time of the disk subsystem. As another type, a disk cache memory adopting a write-back method has been also proposed in JP-A-55-15465. This disk cache memory is arranged to terminate a data write operation only when write data is written in a disk cache memory in response to a data write command issued from a host computer connected to a disk subsystem and then to write the write data to the disk drive.
A direct memory access (DMA) transfer, which corresponds to one method of data transfer between an I/O device and a memory, has been described in an Article of "How an interrupt and DMA are to be done", the Japanese monthly publication "Interface", June, 1989, pp. 223-240, CQ Shuppan-sha, issued on Jun. 1, 1989. The idea disclosed in this article reports that a head address and an area length of a data area to be transferred are just needed to be specified when data is transferred through the effect of the DMA transfer. Hence, one DMA transfer makes it possible only to transfer data on consecutive areas.